I usually will commend the DPS if they're doing well as their described job if I'm another DPS. Sometimes I won't comm if they just go running out the dungeon cuz controller takes some time to get to the menu. This also means you're doing AOE on trash packs, keeping your rotations up. Doing Damage - Those with utility using it as well especially ranged giving mitigation to tanks pulling large pack mobs.

I may not commend if I am leveling and want to get the challenge log XP (but that's not necessary for me anymore).